Comparing analog and digital audio

In analog and digital audio, sound is transmitted and
stored very differently.

Analog
audio: positive and negative voltage

A microphone converts the
pressure waves of sound into voltage changes in a wire: high pressure
becomes positive voltage, and low pressure becomes negative voltage.
When these voltage changes travel down a microphone wire, they can
be recorded onto tape as changes in magnetic strength or onto vinyl records
as changes in groove size. A speaker works like a microphone in
reverse, taking the voltage signals from an audio recording and
vibrating to re-create the pressure wave.

Digital
audio: zeroes and ones

Unlike analog storage media such as magnetic
tape or vinyl records, computers store audio information digitally
as a series of zeroes and ones. In digital storage, the original
waveform is broken up into individual snapshots called samples.
This process is typically known as digitizing or sampling the
audio, but it is sometimes called analog-to-digital conversion.

When
you record from a microphone into a computer, for example, analog-to-digital
converters transform the analog signal into digital samples that computers
can store and process.

Understanding sample rate

Sample
rate indicates the number of digital snapshots taken of an audio
signal each second. This rate determines the frequency range of
an audio file. The higher the sample rate, the closer the shape
of the digital waveform is to that of the original analog waveform.
Low sample rates limit the range of frequencies that can be recorded,
which can result in a recording that poorly represents the original
sound.

Two sample rates

A. Low sample rate that distorts the original sound wave. B. High sample
rate that perfectly reproduces the original sound wave.

To reproduce a given frequency, the sample rate must be at least
twice that frequency. For example, CDs have a sample rate of 44,100
samples per second, so they can reproduce frequencies up to 22,050
Hz, which is just beyond the limit of human hearing, 20,000 Hz.

For the best audio quality, Audition transforms
all audio in 32‑bit mode and then converts to a specified bit depth
when saving files.

Bit depth

Quality level

Amplitude values

Dynamic range

8‑bit

Telephony

256

48 dB

16‑bit

Audio CD

65,536

96 dB

24‑bit

Audio DVD

16,777,216

144 dB

32‑bit

Best

4,294,967,296

192 dB

Higher bit depths provide greater dynamic range.

Measuring amplitude in dBFS

In digital audio, amplitude is measured in decibels
below full scale, or dBFS. The maximum possible amplitude
is 0 dBFS; all amplitudes below that are expressed as negative numbers.

Opmerking:

A given dBFS value does not directly correspond to the original
sound pressure level measured in acoustic dB.

Audio file contents and size

An
audio file on your hard drive, such as a WAV file, consists of a
small header indicating sample rate and bit depth, and then a long
series of numbers, one for each sample. These files can be very
large. For example, at 44,100 samples per second and 16 bits per
sample, a mono file requires 86 KB per second—about 5 MB per minute.
That figure doubles to 10 MB per minute for a stereo file, which has
two channels.

How Adobe Audition digitizes audio

When you record audio
in Adobe Audition, the sound card starts the recording process and
specifies what sample rate and bit depth to use. Through Line In
or Microphone In ports, the sound card receives analog audio and
digitally samples it at the specified rate. Adobe Audition stores
each sample in sequence until you stop recording.

When you play a file in Adobe Audition, the process happens in
reverse. Adobe Audition sends a series of digital samples to the
sound card. The card reconstructs the original waveform and sends
it as an analog signal through Line Out ports to your speakers.

To sum up, the process of digitizing audio starts with a pressure
wave in the air. A microphone converts this pressure wave into voltage
changes. A sound card converts these voltage changes into digital
samples. After analog sound becomes digital audio, Adobe Audition
can record, edit, process, and mix it—the possibilities are limited
only by your imagination.